Diesel fuel



Patented July 2, 1940 UNITED STATES PATENT OFFICE M; Nygaard, Woodbury,N. J

., assignors. to

Socony-Vacnum Oil Company, Incorporated New York, N. Y., a corporationof New York No Drawing.

Application November 8, 1938,

Serial No. 239,506

Claims.

This invention has to do in a general way with fuels for internalcombustion engines of the Diesel or compression ignition type and ismore particularly concerned with the improvement of such fuels by theadmixture therewith of a characterizing ingredient. In an internalcombustion engine operating on the Diesel cycle it is important to theattainment of maximum efliciency that the delay period between theinjection of the fuel and its ignition in the cylinder be short.Improperly delayed ignition gives'rise to the phenomenon known asknocking because of improper coordination between the combustion andcylinder conditions. By decreasing the ignition delay period of a Dieselfuel it is possible to lower the compression pressure at which ignitionof the fuel mixture takes place, thus insuring spontaneous ignitionwithout comoustion shock. This increases the ease of start- Lug and thesmoothness with which combustion takes place, and in addition it permitsless weight )1 mass in the engine design, which makes for lower cost perunit of power output. It will be ieen, therefore, that enhanced speed ofignition Ls a characteristic highly desirable in fuels for ise in Dieselengines.

It has been found that the ignition quality of 1 Diesel or compressionignition fuel can be improved by the addition thereto of small amountsif certain compounds which act as ignition ac- :elerators. This offers ameans for improving ;he better grades of Diesel fuels and also permitswidening the range of available fuels by raising ;he ignition quality ofthe low grade fuels.

The present invention is directed to Diesel ;ype fuels which have beenimproved in ignition uality by the addition of novel compounds which)romote rapidity of combustion and so give the iesired control over thefuels combustion charicteristics. More specifically our invention has LSits object the provision of an improved method if accelerating theignition of liquid hydrocarion fuels in compression ignition engineswhich s} characterized by the admixture with the fuel If a reactionproduct which we will hereinafter 'efer to as a material predominantlycomprised f hydrogen persulfides.

As a material predominantly comprised of hy-- lrogen persulfides ourinvention comprehends the rude reaction products to be hereinafterdecribed, which are comprised of hydrogen perulfides containing sulfurin solution; also those materials obtained as distillates from thiscrude eaction product, which are considered to be a mixture of hydrogenpersulfldes and in addition our invention contemplates materials whichare obtained as the residue from such distillation, such residue being amixture of hydrogen persulfides and sulfur.

Materials of the type just referred to above 5 may be convenientlyprepared by the method described by Walton and Parsons (J. Am. Chem.Soc., 1921, 43, 2539). This procedure involves the steps of preparing asolution of sodium persulfides by dissolving and digesting elementary l0sulfur in a sodium sulfide solution and then acidifying this solution toliberate the hydrogen persulfides. The hydrogen persulfide mixtureobtained from this reaction may be separated from the aqueous solution,and such crude mixture can be used as an improving agent forv Dieselfuels. This crude persulfide mixture may be distilled under vacuum toobtain what we may term purified hydrogen persulfides, which also areeffective improving agents for Diesel fuels, and the residue from suchdistillation may also be employed as an improving agent.

Walton and Parsons report that the crude product of the reactiondescribed above is believed to be a solution of sulfur in equilibriumwith various sulfides of hydrogen and not a.

definite compound and for this reason we have chosen to define suchproduct herein in general chemical terms or by its method of preparationrather than attempting to definitely identify the various constituentcompounds.

The details in one illustrative procedure which may be followed inpreparing the ignition accelerators for Diesel fuel contemplated by thisinvention will be best understood from the following specific example:

The sodium sulfide-sulfur, solution was prepared by dissolving 667 gramsof crystalline sodium sulfide and 100 grams of flowers of sulfur in 267cc. of distilled water. This solution was 40 prepared in a stoppcredflask equipped with a Bunsen valve by heating on a water bath for threehours. The contents of the flask were then slowly added with constantstirring below the surface of two liters of concentrated hydrochloricacid,-whichwas maintained at a temperature between -4 and l0 C. Thecrude hydrogen persulfide mixture thus formed was at first largelypresent as an emulsion but settled to, the bottom of the container overnight. This crude liquid was then separated, washed several timeswithwater, and dried by allowing it to stand in contact with phosphoruspentoxide for. two days. The phosphorus pentoxide was removed byfiltration and a portion of the crude hydrogen persulfide filtrate,hereinafter referred to as product A, was used in preparing a Dieselfuel blend.

The product herein referred to as the purified hydrogen persulfides wasobtained by vacuumdistilling the crudeproduct described above at aliquid temperature of C. and under pressure of 5 mm. The distillate wascollected in two portions, as hydrogen trisulfide and hydro- .gendisulfide,but these two portions were com-.

bined and tested as the product hereinafter referred to as product B.

The residue left after this distillation, which was comprised of amixture of the persulfides and elementary sulfur, was also tested as anignition accelerator for Diesel fuel and is hereinafter identified asproduct C.

To demonstrate the effectiveness of the products contemplated by thisinvention as ignition accelerators for Diesel fuels we have preparedfuel blends containing the products A, B, and C described above and havedetermined the ignition quality of such blended fuel by comparison witha standard reference fuel in a converted C. F. R. engine, using theignition delay method. The results obtained are expressed as Cetanenumbers, which represent the percent by volume of cetane in a blend ofcetane and alpha methyl naphthalene having the same combustioncharacteristics as the sample under test (see Proc. Am. Soc. TestingMaterials, vol. 36 I p. 416, (1936)). An increase in cetane numberindicates an improvement in the combustion characteristics of the fuel.

The results of these'tests, which are indicated in the table, below,were obtained with blends prepared from a Diesel fuel oil having thefollowing characteristics:

The amount of the persulfide product (A,.B or C) in the blend in eachcase is indicated by the percentage of sulfur in the blended oil.

Table I Material blended with 56 PercentS Cetane No. Increase in cetaneNo. fuel 7 in blend of blend cetane No.

Product A 0. 57 59. 5 3. 5 Product Bl 0.47 61 5 Product 0 1.02 62 6 Itwill be apparent from the foregoing table that all of the productscontemplated by this invention, which we have broadly characterized asbeing predominantly comprised of hydrogen persulfides, are effectivewhen admixed with a fuel oil refined for use in a compression ignitionengine to materially improve the ignition quality of the fuel.

It is to be understood that the terms Diesel fuel, Diesel type fuel,hydrocarbon fuel oil," eto., as used-herein are inclusive of any and all.types of hydrocarbon products intended for use in any engine operatingaccording to the Diesel cycle.

We claim:

1. An improved Diesel fuel comprising: a hydrocarbon fuel oil and inadmixture therewith a minor proportion of hydrogen persulfides andelementary sulfur in an amount suflicient to decrease the ignition delayperiod of the fuel.

2. An improved Diesel fuel comprising: a hydrocarbon fuel oil and inadmixture therewith a minor proportion of hydrogen persulfides in anamount sufficient to decrease the ignition delay period of the fuel.

4 3. An improved Diesel fuel comprising: a hydrocarbon fuel oil and inadmixture therewith a minor proportion of a crude hydrogenpersulfide-sulfur mixture obtained by digesting a water solution ofsodium sulfide and elementary sulfur at an elevated temperature;acidifying the reaction mixture with hydrochloric acid to form thehydrogen persulfide-sulfur mixture; and separating said mixture from theaqueous solution, said mixture being present in the oil in an amountsufficient to decrease the ignition delay period of the fuel.

4. An improved Diesel fuel comprising: a hydrocarbon fuel oil and inadmixture therewith a minor proportion of purified hydrogen persulfidesobtained by digesting a water solution of sodium sulfide and elementarysulfur at an elevated temperature, acidifying the reaction mixture withhydrochloric acid to form crude hydrogen persulfides, separating thecrude hydrogen persulfides from the aqueous solution, washing and dryingthe crude hydrogenpersulfides, and distilling the crude hydrogenpersulfides under vacuum at a liquid temperature in the neighborhood of120 C.- to obtain the purified hydrogen persulfides, said purifiedhydrogen persulfides being present in the oil in sufficient amount todecrease the ignition delayperiod of the fuel.

5. An improved Diesel fuel comprising: a hydrocarbonv fuel oil and inadmixture therewitl". a minor proportion of the residue obtained fromthe distillation under vacuum at a liquid temperature in theneighborhood of 120 C. of th( reaction product obtained by digesting awatei solution of sodium sulfide and elementary sulfur at an elevatedtemperature, acidifying thl product thus obtained with'hydrochloric acidanc then separating the aqueous solution from tht crude product to bedistilled, said residue being present in the oil in an amount sufiicientto decrease the ignition delay period of the fuel.

6. An improved Diesel fuel comprising: a hy drocarbon fuel oil and inadmixture therewith minor proportion of a crude hydrogen per-sulfidesulfur mixture obtained by digesting a water so lution of about 6.7parts of sodium sulfide am about one part of elementary sulfur at anelevatei temperature; acidifying the reaction mixture wit] hydrochloricacid to form the hydrogen persul fide-sulfur mixture; and separatingsaid mix ture from the aqueous solution, said mixture bein present inthe oil in an amount sufficient to de crease the ignition delay periodof the fuel.

7. An improved Diesel fuel comprising: a hy drocarbon fuel oil and inadmixture therewith minor proportion of purified hydrogen persul fidesobtained by digesting a water solution c about 6.7 parts of sodiumsulfide and about on part of elementary sulfur at elevated tempera ture,acidifying the reaction mixture with by drochloric acid to form crudehydrogen persui fides, separating the crude hydrogen persulfide from theaqueous solution; washing and drying the crude hydrogen persulfides; anddistilling the crude hydrogen persulfides under vacuum, at aliquidtemperature in the neighborhood of 120 C. to obtain the purifiedhydrogen persulfides, said purified hydrogen persulfides being presentin the oil in sufficient amount to decrease the ignition delay period ofthe fuel.

8. The method of accelerating the ignition of liquid fuels for internalcombustion engines of the type wherein ignition o1 the fuel isspontaneously effected by injection into the compressed air in theengine cylinder which comprises admixing with the fuel prior to ignitiona minor proportion of a material predominantly comprised of hydrogenpersulfides.

9. The method oiacceleratlng the ignition oi liquid fuels for internalcombustion engines of the type wherein ignition 01' the jtuel isspontaneously effected by injection into the compressed air in theengine cylinder which comprises admixing with the fuel prior to ignitiona minor proportion of a material comprised of hydrogen persulfldes andsulfur.

10. The method of accelerating the ignition of liquid fuels for internalcombustion engines of.

the type whereineignition of the fuel is spontaneously effected byinjection into the compressed air in the engine cylinder which comprisesadmixing with the fuel prior to ignition a minor proportion of hydrogenpersulfides.

HENRY G. BERGER.

RICHARD S. GEORGE. EDWIN M.- NYGAARD.

